The present invention relates to yarn texturing methods and apparatus. More particularly, it relates to yarn texturing using stuffing box techniques.
It is well known to use stuffer box crimpers in the production of textured yarn. In accordance with one stuffer box technique, uncrimped yarn is transported by a pair of counter-rotating nip rolls into and through a confined zone known as a stuffer box. In the box the yarn is caused to be folded and compressed into a fine crimp configuration. The crimp in the yarn is heat set to make it of a lasting nature. The yarn moves through the box in compact plug-like form. In a second stuffer box technique, it has been found advantageous to employ a flow of hot compressible fluid to convey the yarn into and through the box instead of using nip rolls. In order to obtain a more permanent crimp in the yarn, the movement of the yarn through the box is often restricted by suitable counter-pressure means, for instance a flap or a plunger. Where the yarn is advanced vertically upward; the weight of the plug of yarn and surface friction can provide suitable counter-pressures and the use of a flap, plunger or the like is not required. It is quite important that the height of the plug in the confined zone remain uniform and not go above or below predetermined close limits. Otherwise, the crimp and, thus, bulk will vary considerably in uniformity; and the quality of textile articles made from the resulting yarn will be inferior.
There are many causes for the occurrences of plug height variations. Among these causes are unevenness of the denier of the source yarn, buildup of deposit of degraded yarn finish on the inner surfaces of the confined zone defining means, and variations occurring in the rates at which the yarn transport means conveys the yarn into and from the texturing operation.
Quite often the source yarn is first wound on interim bobbins. Such bobbins are stocked on a creel; and the yarn is fed to the texturizer by being withdrawn overend from a bobbin. Obviously, such removal causes a small amount of twist to be imparted to the yarn. Unfortunately, the amount of twist increases in a direct relation to the amount of yarn withdrawn. This variation in twist in yarn moving from the outside of the package to the inside of the package is called "twist bias". With a normal size bobbin of heavy denier yarn, twist varies from 0.02 to 0.05 turn per inch; or, stated another way, there is a 150% increase of twist imparted to the yarn during overend withdrawal from the bobbin. With the increasing amounts of twist, there is a steady and gradual decrease in plug height.
In stuffer box compressive crimping, there are many known devices that sense the yarn plug level by photoelectric cells, pneumatic sensing devices, mechanical sensing devices or combinations thereof and in response control the speed of the driven yarn forwarding rolls or withdrawal rolls. The known plug control devices are quite complex in structure and operation and are expensive to maintain.
Where jet stuffer box texturing is used, it has been suggested in U.S. Pat. No. 3,886,636 to control the plug height level by either adjusting the temperature of the yarn prior to or during the crimping step by varying the temperature of the fluid jetting the yarn into the box in response to a sensed change in plug height level. This non-isothermal approach for maintaining a uniform plug height level, unfortunately, senses the presence of twist bias as an increase in bulk and responds by reducing the temperature of the fluid. This temperature change causes a real decrease in bulk to maintain the predetermined plug height level resulting in a bulk bias through the package of textured yarn.
An objective accomplished by the present invention is the provision of a stuffer box texturing system wherein the plug height level is maintained by a device of simple construction with no moving parts. Yarns textured by such system have improved uniformity of bulk from one bobbin to another and from the outside to the inside of a given bobbin.